Seals, such as O-rings, are commonly used in equipment that use or process fluids. The O-rings can be used in cylindrical chambers to seal the chambers at joints or unions around an interior perimeter of the chamber. Such O-rings can be used to help seal the perimeter the container while still allowing movement of the contents of the chamber within its interior without obstruction. One type of O-ring seal that can be useful in applications that seal a moving cylinder, such as a shaft or a piston, within a bore of a housing is an O-ring with a U-shaped profile, or a U-seal. For example, U-seals are commonly used in hydraulic cylinders.
The U-Seal design can also be made to work in same applications where there is a sliding shaft or piston that has one or more cross-bores that can interact with the seal. An inherent problem lies in the bores crossing over the seals. A conventional U-seal is employed in applications where the extrusion gap (distance between the U-seal and the shaft or piston) is kept to a constant small distance along the entire surface of the cylindrical U-seal. This distance is typically a value around 0.001 inches to 0.005 inches per side or in the radial direction. If the extrusion gap of the seal is not kept to a minimum the inner lip, or arm, of the U-seal has a tendency to roll over or tear. This problem is increased significantly if a cross bore resides in the shaft or piston being sealed.
In a typical U-seal inside of a housing or bore, the fluid pressure fills the U-shaped cavity of the U-seal and applies a sealing pressure against the piston sliding across the seal keeping the fluid from leaking out of the apparatus. This is a common practice for items such as hydraulic cylinders. When the piston that has a hole, or bore, through it is sealed by the typical U-seal and that bore crosses over the seal, problems will occur. For example, the extrusion gap principle is lost and the seal no longer has a surface to ride against to keep the seal in position. Thereby, the seal is allowed to relax. When the seal is relaxed, it is allowed to protrude into the housing or bore where the seal will likely be torn or damaged when caught between the edge of the bore in the piston and the edge of the housing. For example, when the bore extends across a large portion of the seal, the sharp edges of the bore begin to slide into the exposed part of the U-Seal that is protruding into the housing, causing the seal to fail prematurely.